The invention relates to a device for measuring the rotating angle of two objects rotating around an axis in relation to each other, in accordance with the preamble of patent claim 1.
Identifying the rotating angle of two objects rotating around an axis in relation to each other, for example, the rotating angle of a motor shaft rotating relative to a stationary element, may take place with the aid of a contact-free optical sensor, as based on the polarizing properties of light. Examples of such devices are disclosed by DE 201 02 192 U1, EP 2 187 178 A1, EP 1 507 137 A1, or U.S. Pat. No. 7,777,879.
Devices known to the prior art for measuring the rotating angle of two objects rotating around an axis in relation to each other have a light source assigned to one of the objects; a polarizer assigned to the other object, such that the light source and the polarizer rotate in relation to each other as function of the rotating angle; and a receiver which measures the reflected luminous intensity, or that which passes through the polarizer, in order to produce a signal dependent on the rotating angle. Here the receiver has an initial reception element, and the light emitted by the light source is either polarized or becomes polarized, and/or a polarizing filter with an initial direction of polarization is positioned in front of the first reception element. The relative rotation between a light beam polarized in linear fashion and a linear polarizer brings about a modulation of the luminous intensity. This modulation can be detected by a receiver, and from said modulation the relative angular positioned can be determined. If the polarizer is positioned on a rotating object, e.g., a motor shaft, the rotating angle of the rotating object can be determined. Based on the physical properties of the polarization, the angle-dependent signals have two periods per rotation over 360°, with the result that there is an incremental signal, but not an absolute signal.
Known from US 2005/211886 A1 and GB 1 498 409 A are devices for measuring the rotating angle of two objects rotating in relation to each other around an axis, which devices have a light source and a polarizer which rotate in relation to each other as a function of the rotating angle and, further, have a receiver which measures the luminous intensity passing through the polarizer, in order to produce a signal that is dependent on the angle of rotation. Here each receiver has at least one reception element, in front of which there is positioned a polarizing device with an initial polarization direction, while an element that casts a shadow is positioned in front of the receiver. Here the receiver has at least one quadrant diode, and means are provided for varying the shape of the shadow on the receiver over a rotation of 360°.
The goal of the invention, therefore, is to provide clarity of measurement over a full rotation of 360° for the rotating object and thus to provide an absolute angular signal, with as small as possible a loss in signal quality.
This goal is achieved with a device for measuring the rotating angle of two objects rotating in relation to each around an axis and with a process for measuring the rotating angle of two objects rotating in relation to each other around an axis.
Advantageous embodiments and elaborations of the invention are specified in the dependent claims.